1. Field of the Invention
The present invention relates to a through hole formation method using the Si anisotropic etching which is useful for the formation of an acceleration sensor, the ink supply opening of an ink jet head, or the like, that may require the micromachining techniques.
2. Related Background Art
As one of the conventional micromachining techniques, there has been widely adopted the anisotropic etching using alkaline solution to process the Si substrate which is provided with the &lt;100&gt; crystal plane orientation. This etching utilizes the difference in the dissolving speeds into the alkaline solution in accordance with the plane orientations. More specifically, the etching is in progress in a mode that the plane &lt;111&gt; where the dissolving speed is extremely slow is left intact.
FIG. 5 is a cross-sectional view schematically showing the example of a processed section formed by the conventional Si anisotropic etching. In FIG. 5, a reference numeral 51 designates an Si substrate; 52, an etching mask; 53, a &lt;100&gt; plane; and 54, a &lt;111&gt; plane. As shown in FIG. 5, the &lt;111&gt; plane is angled at approximately 55.degree. both to the plane orientations of the &lt;100&gt; plane 53. As a result, in accordance with the conventional Si anisotropic etching, it is required to provide a width of (X+2t/tan 55.degree.) geometrically for the initiation surface of the object to be etched in order to obtain a width X of a desired penetration process if the Si substrate 51 having a thickness t should be processed penetratingly, for example. There is then a limit to the configuration that may be processed by the adoption of such conventional art, therefore the process is largely restricted. Also, when such anisotropic etching method is applied to forming the ink supply opening of an ink jet head, or the like, for example, this method tends to impede making the chip smaller or present hindrance to the post processing of a chip (such as in the die bonding) eventually.